1. Field of the Invention
This invention is related to shoe machines and more particularly to heating devices for heating portions of shoe uppers prior to molding such portions.
2. Prior Art
Devices for heating and molding portions for shoe uppers generally comprise an inner form and a cooperating outer band, with motive means for effecting relative movement between the inner form and the outer band, where a shoe upper placed therebetween may be clamped therebetween. Heating and molding devices may also include a first heating means for heating the inner form and a second heating means for heating the outer band, the second heating means comprising a radiant heater arrangement to which the outer surface of the outer band is exposed. Such a device may be found in the U.K. Patent Specification Number 1,186,875. A commercial embodiment of the above described device utilizes a radiant heater means by which the outer band is heated and controlled by a simmerstat, that is, by heater means which is switched on and off on a timed basis. In order to protect the outer band from over heating, and consequent degradadation, the heater timer means has to be set so that the outer band can not be heated above the degradadation temperature of the material of the outer band.
When the heater device is in use, however, heat is drained quickly from the outer band when it brought into a clamping engagement with a relatively cold shoe upper portion. When the device is in use, heat is drained quickly from the outer band when it is brought into clamping engagement with a relatively cold shoe upper portion. If such contact takes place during the time when the heater switching means has switched the heater means off, no heat in the outer band is replaced, with a result that insufficient heat is supplied into the shoe upper portion from the outside. It is desireable, especially for actuating thermoplastic stiffeners, or stiffeners coated with a thermoplastic material, that the heat be applied through the whole thickness of the thermoplastic material. It has been necessary in the heating device being described, to rely to a larger extent upon the supply of heat from the inner form. In order to heat through the thickness of the thermoplastic material, however, by heat largely supplied from the inside the shoe upper portion, excessive heat may be applied, which can lead to damage to the lining of the shoe upper portion. If, on the other hand, precautions are taken to avoid damage to the lining of the shoe upper, then it may be that insufficient heat is applied from the linear rather from the inner form.
It is an object of the present invention to provide an improved heater device in which a suitable balance of heat can be supplied from the inside form as well as from the outside form to a shoe upper portion therebetween.